I've got a 1998 Cherokee 148xxx.
On a cold start she sounds great but after a few minutes/warms up a steady light knock starts up. It almost sounds like a rattle can. It doesn't get louder when i accelerate and I don't have a loss of power . It sound like it's coming from the beginning of the transmission or maybe even the bottom end of the engine.

The front of the teeth of the flexplate have small wear marks so I thought maybe the starter was rubbing. I changed the starter no luck. I even started it then took the starter completely off while it was running but she was still knocking.

So all in all I've checked for cracks in the flexplate, tightened the flexplate bolts with loctite and changed the starter with no luck. Any ideas?

 

Is it possibly the very common exhaust rattle on the crossmember?

 

I've checked for that as well the exhaust is tight and clear of everything. If I'm listening to the engine under the hood I can barely hear it but when I'm standing on the driver side and passenger side it's a very noticeable knock. When I'm up underneath it sounds like it's right where the tranny and engine meet

 

It sounds like you've got the usual suspects covered then - exhaust hitting the cross-member, flex plate loose, etc.

Is it possibly the catalytic converter? (Thinking the catalyst loose and rattling...)

Perhaps someone smarter than myself can advise further.

 

Possibly the purge valve solenoid next to the firewall

 

lean misfire?